Publications

2000

• Molecular dynamics study of the solid–liquid interface
  
  • Geysermans P.
  • Gorse D.
  • Pontikis V.
  The Journal of Chemical Physics, American Institute of Physics, 2000, 113 (15), pp.6382-6389. (10.1063/1.1290730)
  DOI : 10.1063/1.1290730
• Automatic object identification: an fMRI study.
  
  • Boucart M.
  • Meyer M. E.
  • Pins D.
  • Humphreys G. W.
  • Scheiber C.
  • Gounod D.
  • Foucher J.
  NeuroReport, Lippincott, Williams & Wilkins, 2000, 11 (11), pp.2379-83. Boucart and Humphreys reported an automatic access to object identity when observers attend to a physical property of the form of an object (e.g. the orientation) but not to its colour. We sought evidence for automatic identification in a brain imaging study using fMRI. In an orientation decision task participants decided whether a picture was vertical or horizontal. In the colour decision task participants decided if a picture was blue or green. Activation of areas 18-19 was found for both color and orientation. Activation of the temporal area 37 occurred more frequently in the orientation than in the colour decision task. This result suggests that automatic identification activates the same brain area as overt processing of semantic information.
• Imaging the vortex-lattice melting process in the presence of disorder
  
  • Soibel A.
  • Zeldov Eli
  • Rappaport Michael
  • Myasoedov Yuri
  • Tamegai Tsuyoshi
  • Ooi Shuuichi
  • Konczykowski Marcin
  • Geshkenbein Vadim B.
  Nature, Nature Publishing Group, 2000, 406 (6793), pp.282-287. General arguments(1) suggest that first-order phase transitions become less sharp in the presence of weak disorder, while extensive disorder can transform them into second-order transitions; but the atomic level details of this process are not clear. The vortex lattice in superconductors provides a unique system in which to study the first-order transition(2-6) on an inter-particle scale, as well as over a wide range of particle densities. Here we use a differential magneto-optical technique to obtain direct experimental visualization of the melting process in a disordered superconductor. The images reveal complex behaviour in nucleation, pattern formation, and solid-liquid interface coarsening and pinning. Although the local melting is found to be first-order, a global rounding of the transition is observed; this results from a disorder-induced broad distribution of local melting temperatures, at scales down to the mesoscopic level. We also resolve local hysteretic supercooling of microscopic liquid domains, a nonequilibrium process that occurs only at selected sites where the disorder-modified melting temperature has a local maximum. By revealing the nucleation process, we are able to experimentally evaluate the solid-liquid surface tension, which we rnd to be extremely small. (10.1038/35018532)
  DOI : 10.1038/35018532
• Etude structurale et cristallographie des composés du ciment anhydre.
  
  • de Noirfontaine Marie-Noëlle
  , 2000. Cette étude structurale sur les composés du ciment anhydre a principalement porté sur le composé majoritaire, l'alite (silicate tricalcique impur), dont l'hydratation produit la fraction la plus importante de l'effet de colle du ciment hydraté. Le silicate tricalcique, C3S, présente un polymorphisme dépendant à la fois de la température et des impuretés qu'il contient. Les sept variétés de polymorphes sont de symétries tricliniques (formes appelées T1, T2, T3), monocliniques (M1, M2, M3) et rhomboédrique (R). Dans les clinkers industriels, les alites stabilisées sont essentiellement de symétries monocliniques. L'identification du polymorphe présent est difficile par diffraction des rayons X parce que les diagrammes de poudre sont très semblables. Pourquoi certaines impuretés stabilisent-elles une forme plutôt qu'une autre ? Y a-t-il un lien entre la structure observée et la réactivité du clinker ? Il faut s'appuyer sur une bonne connaissance structurale des différents polymorphes pour tenter de répondre à ces questions.
• Characterization of Li-colloids in electron-irradiated Li2O-crystals by neutron scattering
  
  • Vajda P.
  • Beuneu F.
  • Krexner G.
  • Prem M.
  • Blaschko O.
  • Maier C.
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2000, 166, pp.275. Lithium oxide crystals containing metallic Li-colloids created by MeV-electron irradiation around room temperature were analyzed by elastic neutron scattering. High-resolution scans on a triple-axis spectrometer show that the main Bragg peaks of the irradiated Li2O crystals are broadened and exhibit diffuse shoulders due to the introduced lattice damage. Extensive search in reciprocal space reveals the presence of weak, yet well-defined, point-like intensities which can be identified as Bragg reflections of bulk bcc lithium. The Li precipitates are aligned according to the orientational relation [1 1 0]Li//[1 1 1]Li2O and may correspond to the large (>1 µm) Li-colloids observed earlier by conduction electron spin resonance (CESR) and by optical microscopy. Small-angle neutron scattering on the same crystals indicates an anisotropic distribution of non-spherical precipitates whose diameters lie in the range of several hundred angstroms and which possibly represent the small Li-colloids ("1 µm) characterized by CESR. (10.1016/S0168-583X(99)00663-1)
  DOI : 10.1016/S0168-583X(99)00663-1
• Magnetic relaxation in the "Bragg-glass" phase in BSCCO
  
  • van Der Beek C.J.
  • Colson S.
  • Konczykowski M.
  • Indenbom M.V.
  • Drost R.J.
  • Kes P.H.
  Physica C: Superconductivity and its Applications, Elsevier, 2000, 341-348 (PART 3), pp.1279. Magnetic relaxation in the Bragg-glass phase of overdoped Bi2Sr2CaCu2O8 crystals was investigated using time-resolved magneto-optical visualisation of the flux distribution. This has permitted us to extract the current-voltage characteristic, which can be well described by a power-law, although fits to a stretched exponential E ~ exp(- jc/j)µ with 0.3 < µ < 0.8 are passible at long times in excess of 100 g. © 2000 Elsevier Science B.V All rights reserved.
• On-site magnetization in open antiferromagnetic chains: A classical analysis versus NMR experiments in a spin-1 compound
  
  • Botti Silvana
  • Rosso A.
  • Santachiara R.
  • Tedoldi F.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2000, 63, pp.012409. The response of an open spin chain with isotropic antiferromagnetic interactions to a uniform magnetic field is studied by classical Monte Carlo simulations. It is observed how the induced on-site magnetization is nonuniform, due to the occurrence of edge staggered terms which decay exponentially over a distance equal to the zero-field correlation length of the infinite chain. The total magnetic moment associated to each staggered term is found to be about half of the original single-spin magnitude and to decrease as the inverse of temperature (i.e., to behave as a Curie-like moment). The numerical results are compared to recent NMR findings in spinless-doped Y2BaNiO5; the remarkable agreement found shows that, for temperatures above the Haldane gap, the classical approach gives a correct picture of the boundary effects observed in the Heisenberg S=1 chain. (10.1103/PhysRevB.63.012409)
  DOI : 10.1103/PhysRevB.63.012409
• Ab initio calculations of response properties including electron-hole interaction
  
  • Olevano Valério
  • Albrecht Stefan
  • Reining Lucia
  , 2000. We discuss the current status of a computational approach which allows to evaluate the dielectric matrix, and hence electronic excitations like optical properties, including local field and excitonic effects. We introduce a recent numerical development which greatly reduces the use of memory in such type of calculations, and hence eliminates one of the bottlenecks for the application to complex systems. We present recent applications of the method, focusing our interest on insulating oxides.
• Synthesis of soluble polymers for medicine that degrade by intramolecular acid catalysis
  
  • Dubois-Clochard Marie-Claude
  • Rankin Sheila
  • Brocchini Steve
  Macromolecular Rapid Communications, Wiley-VCH Verlag, 2000, 21 (12), pp.853–859.
• Do Columnar Defects Produce Bulk Pinning?
  
  • Indenbom M.V.
  • van Der Beek C.J.
  • Konczykowski M.
  • Holtzberg F.
  Physical Review Letters, American Physical Society, 2000, 84 (8), pp.1792. From magneto-optical imaging performed on heavy-ion-irradiated YBa2Cu3O7-d single crystals, it is found that at fields and temperatures where strong single vortex pinning by individual irradiation-induced amorphous columnar defects is to be expected, vortex motion is limited by the nucleation of vortex kinks at the specimen surface. In the material bulk, vortex motion occurs through (easy) kink sliding. Depinning in the bulk determines the screening current only at fields comparable to or larger than the matching field, at which the majority of vortices is not trapped by an ion track.
• Bose-glass melting in the cubic (K,Ba)BiO3 high-Tc oxide with columnar defects
  
  • Klein Thierry
  • Conde-Gallardo A.
  • Joumard I.
  • Marcus J.
  • van Der Beek C.J.
  • Konczykowski M.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2000, 61 (6), pp.R3830. The Bose-glass transition in the fully isotropic (K,Ba)BiO3 superconductor with columnar defects produced by irradiation with 7.2 GeV Ta ions was studied by transport and nonlinear susceptibility measurements. For fields smaller than the dose equivalent field Bφ, the Bose-glass transition line HBG(T) shifts progressively upwards with increasing dose, dHBG/dT∼1+αBφ1/2. The critical exponents have been deduced from the scaling properties of the transport measurements; we obtain z = 5.3±0.3 and ν=1.1±0.2. For tilted magnetic fields, the transition temperature scales as TBG(0)-TBG(θ)∼/sin(θ)1/ν, as recently suggested by Lidmar and Wallin. ©2000 The American Physical Society.
• Current-enhanced anisotropy of Bi2Sr2CaCu2O8 in the mixed state
  
  • Khaykovich B.
  • Myasoedov Y.N.
  • Teitelbaum K.
  • Zeldov E.
  • Fuchs D.T.
  • Tamegai T.
  • Ooi S.
  • Konczykowski M.
  • Rycroft S.F.W.R.
  Physica C: Superconductivity and its Applications, Elsevier, 2000, 341-348 (PART 3), pp.985. Transport and local magnetization measurements carried out simultaneously in Bi2Sr2CaCu2O8 (BSCCO) crystals reveal finite resistivity well below the magnetic irreversibility line, where the vortices should be pinned. This resistivity is non-monotonic with temperature and extremely non-linear. We describe the new observation in terms of a shear-induced decoupling, in which the pancake vortices flow only in the top few layers and are decoupled from the pinned vortices in the rest of the crystal. COP. 2000 Elsevier Science B.V. All rights reserved.
• Erratum: Atomic Structure and Vibrational Properties of Icosahedral B 4 C Boron Carbide [Phys. Rev. Lett. 83, 3230 (1999)]
  
  • Lazzari R.
  • Vast N.
  • Besson J. M.
  • Baroni S.
  • Dal Corso A.
  Physical Review Letters, American Physical Society, 2000, 85 (19), pp.4194 - 4194. (10.1103/PhysRevLett.85.4194)
  DOI : 10.1103/PhysRevLett.85.4194
• Entropy, vortex interactions and the phase diagram of heavy-ion irradiated Bi2Sr2CaCu2O8+δ
  
  • van Der Beek C.J.
  • Konczykowski M.
  • Drost R.J.
  • Kes P.H.
  • Samoilov A.V.
  • Chikumoto N.
  • Bouffard S.
  • Feigel'Man M.V.
  Physica C: Superconductivity and its Applications, Elsevier, 2000, 332 (1), pp.178. Using dynamic and thermodynamic magnetization measurements, we analyze the phase diagram of Bi2Sr2CaCu2O8+δ single crystals containing amorphous columnar defects created by heavy-ion irradiation. Reversible magnetization experiments yield the respective magnitudes of the pinning energy and entropy contributions to the free energy of the vortex lattice. It appears that the entropy contribution in the London regime is relatively minor in both unirradiated and irradiated crystals, except in the case of high density of columns and inductions B that are smaller than the interaction field Hint≈Bφ/6. The dependence of the entropy contribution on vortex and defect density correlates well with measurements of the irreversibility line (IRL) Hirr(T), which shows a sharp increase at Hint. (10.1016/S0921-4534(99)00663-2)
  DOI : 10.1016/S0921-4534(99)00663-2
• SANS study of the microstructural evolution of martensitic steels under thermal ageing and neutron irradiation
  
  • Mathon M.H.
  • Geoffroy G.
  • de Carlan Y.
  • Alamo A.
  • de Novion C.H.
  Physica B: Condensed Matter, Elsevier, 2000, 276-278 (1), pp.939. SANS technique has been used to study the microstructural evolution of martensitic steels containing 7-12% Cr, under thermal ageing and neutron irradiation. Some of the investigated alloys are industrial low activation martensitic (LAM) materials, where alloying elements have been substituted by elements with low radiological impact. For materials quenched from the austenitic phase, a direct correlation was found between the hardening and the number density of M2C precipitates induced by thermal ageing at 500 °C. Irradiation-accelerated spinodal decomposition of the B.C.C. ferrite was observed in alloys containing large (= 11%) chromium content. (10.1016/S0921-4526(99)01299-5)
  DOI : 10.1016/S0921-4526(99)01299-5
• Interplay of pancake vortices and columnar defects in heavy-ion irradiated Bi-2212
  
  • Drost R.J.
  • Kes P.H.
  • van Der Beek C.J.
  • Konczykowski M.
  Physica C: Superconductivity and its Applications, Elsevier, 2000, 341-348 (PART 3), pp.1167. An analysis of equilibrium magnetization curves of Bi2Sr2CaCu2O8+d with different doses of columnar tracks reveals the distribution of pancake vortices on columnar pinning sites. In addition, core pinning is found to be the prevailing interaction mechanism between pancake vortices and columnar defects. © 2000 Elsevier Science B.V. All rights reserved.
• Magnetic relaxation in the vicinity of second magnetization peak in BSCCO crystals
  
  • Konczykowski M.
  • Colson S.
  • van Der Beek C.J.
  • Indenbom M.V.
  • Kes P.H.
  • Zeldov E.
  Physica C: Superconductivity and its Applications, Elsevier, 2000, 332 (1), pp.219. We have used Hall array and magneto-optic techniques for the investigation of magnetic relaxation in clean Bi2Sr2CaCu2O8 (BSCCO) crystals. The enhancement of the bulk critical current seen as a second peak in the magnetization curves is identified with the discontinuous change of the flux creep energy barrier vs. current relation. We propose a consistent interpretation of the hysteretic magnetization and its relaxation in clean BSCCO crystals, based on the presence of two distinct vortex matter phases, manifesting different electrodynamics. Special attention will be given to the motion of the interface between those phases across the sample. (10.1016/S0921-4534(99)00675-9)
  DOI : 10.1016/S0921-4534(99)00675-9